Descriptions of British Diptera. 36 J 



heat of the day, and are therefore most troublesome to cattle and 

 beasts of burden where they stand most in need of repose. They 

 are particularly excited and eager for blood when the atmosphere is 

 in a warm and humid state, such as it usually is after a thunder 

 shower. It is invariably observed to be the females that attack 

 animals, the males being usually found on flowers from which they 

 extract the juices ; * both sexes, indeed, have been known to feed 

 on a saccharine liquid. The quantity of blood which they can gorge 

 is much more considerable than might be supposed from the size of 

 the body, as the latter, after a full meal, becomes dilated beyond 

 its usual dimensions. Several of them attack indiscriminately many 

 different kinds of the larger quadrupeds, especially the ruminants, 

 but others, like the CEstri, more particularly attach themselves to 

 certain species. Thus, the rein-deer has a winged parasite appro- 

 priated almost exclusively to itself; and it is not improbable that 

 a more extensive knowledge of the history of these flies would make 

 us acquainted with others equally restricted in the choice of their 

 victims. 



The oral organs of the Tabani are very highly developed, consti- 

 tuting an apparatus for extracting the blood, of a somewhat com- 

 plex structure, but admirably adapted to the purpose. It resembles 

 a case of lancets, having all the parts so formed and adjusted to 

 each other, that they serve at the same time to pierce the skin, and 

 to form a tube for the passage of the fluid. Although so dissimilar 

 in shape, these parts are found to correspond in number and situa- 

 tion to the oral appendages of the Coleoptera. The concave lobes 

 of the lip probably enable the insect to attach itself firmly, and to 

 render the apparatus steady ; while the palpi are useful in divid- 

 ing the hair, and form a kind of protecting sheath for the other 

 parts when they are unemployed. In substance the pieces are so 

 stiff and horny, that they easily make their way through the hard- 

 est and coarsest hide. 



These insects deposit their eggs in the earth. The larva of one 

 of the species, (7*. bovinus) has been figured and minutely described 



by De Geer. It is long, cy- 

 lindrical, and rather slender, 

 narrowing at the head into 

 an elongated cone, and bear- 

 ing much resemblance to those 

 of some of the larger Tipuli- 

 dae which live in the earth. 



" The same fact has been noticed in relation to the respective sexes of va- 

 rious Culices, and some other sanguisugous species. 



